56 PROCEEDINGS OF THE NATIONAL MUSEUM

Sphyrna media

differs

from

S.corona in

having

a narrowerpostor- bital processto the chondrocranium, with the anterior edge of this structure posterior, rather than anterior, to the angle

formed by

the junctureoftheinnerorbital

and

anteriormediorbitalcartilages^(pi.7c)

;

a slightly deeper anterior fontanelle;

and

shorter rostral cartilages.

The

last differencehas

been

objectively

shown by

dividing the trans- verse distance

between

the tips of the preorbital cartilages into the

Figure14.

—

Sphyrnaviedia:a,adult male,900mm.TL,fromPanamaBay(UCLA58-304);

b,headofsamespecimen, about0.12X;c,dermaldenticles ofsamespecimen;d,upper andlowerteeth,left side,ofsamespecimen, about1.5 X. (DrawingsbyDorothea B, Schultz.)

lengthoftherostral cartilage.

For

S.

media

therangeofvaluesthus obtained is

from

18.1 to 24.0 percent,

and

for S. corona

from

25.9 to 30.5percent;these

have been

plotted

and may

be seeninfigure 17.

Sphyrna media

also differs

from

S. corona in

having

a slightly shortersnout.

A comparison

ofsnout lengths

may be

seenin figures 156, 16,

and

186.

Although

there is

some

overlap in values for the

two

species,

when

specimensofa

comparable

sizeare

compared

lower valuesareobtainedfor S.media.

HAMMERHEAD SHARKS — ^GILBERT 57 Sphyrna media

also differs

from

S. coronain having:

The

anal fin

more

deeply falcate

and

with a

more

pointed apex (figs. 14a, 15a);

anterior-median pore patch

on

underside of

head

with the posterior

margin more

broadly

rounded and

with a pointed median-posterior extension (fig. 22/)^; a

more

pointed

upper

precaudal pit in smaller specimens (fig. 21g);

and

aslightly wider

mouth. When

thetrans- verse distance

between

the corners of the

mouth

is divided

by

the

head

width, the values obtained are

somewhat

greater for S.

media

Finally,

Sphyrna media may be

a larger species.

The

largest

specimen

of

Sphyrna media

seen (a head)

was

calculated to

be

1025

mm. TL,

while of the 17 specimens of

Sphyrna

corona examined, thelargest (theholotype)

measured

only 672

mm. More

specimensof S.corona

must

be seentodefinitelyconfirmthis,however.

A comparison

of

Sphyrna media

with other

members

ofthegenusis

presentedintable 1.

Description.^

—

-Meristicdataappearintable 7. Characters

men-

tionedin thediagnoses ofthe

subgenus

Platysqualus

and

of S.

media

arenot repeatedhere.

FigureIS.

—

Sphyrna media:a,juvenilefemale,356mm.TL,from Chiapas,Mexico

(FMNH

63093);b,headofsamespecimen. (DrawingsbyPaulLaessle.)

Head moderately

expanded, the greatest

width measuring from

22.3 to 27.3 percent of

TL;

character of anterior-median

margin

of

head somewhat

variable,evenly

rounded

in

some

individuals,with

no

median

indentation,

and

with a broad, very shallow

median

depres- sion in others; outer posterior corner of lateral expansion of

head

situated anterior tocornerof

mouth;

narialflapbroad,bluntly pointed attip, with the broadly curved outer edge curving sharply inward; a

58 PROCEEDINGS OF THE NATIONAL MUSEUM

^{vol. ii9}

very shortlabialfurrow presentatcorneroflower

jaw

inlarger speci- mens, not noticeableinsmaller specimens.

Origin offirst dorsal fin slightly posterior to axil of pectoral fin, aperpendicularline

drawn

ventrally

from

originintersectinganterior third of pectoral fin; base of first dorsal fin one-third to one-half lengthof

head and

about twice length of pectoralfinbase; anterior

margin

of first dorsal fin broadly

and

evenly curved, particularly in larger individuals; distal

margin

of first dorsal fin rather deeply falcate, particularly

on

lower two-thirds of fin; lobe of first dorsal fin

from

two-fifths to one-half length offirst dorsal base; origin of second dorsal fin situated

about

two-fifths of

way back above

base of anal fin; second dorsal fin tall, its greatest height

about

three- fourths lengthofbase

and from

three-fourths to four-fifths of greatest heightofanalfin; seconddorsalfinbase

from

one-half to five-eighths ofanalfinbase; lobe ofseconddorsalfinratherlong, itslength

about

a third again greatest height of fin

and

extending

from

two-thirds to three-fourths of distance

from

posterior part of second dorsal baseto

upper

precaudalpit;pectoral fin

from

two-fifths to two-thirds length of

head

(higher values usually apply to larger individuals)

;

pectoral fin two-thirds as

broad

aslong; lengthof pectoral finbase

from

five-eighthsto thi'ee-fourthslengthof analfinbase; inner two- thirds of anterior

margin

of pectoralfinstraight, outerthird slightly convex;distal

margin

ofpectoralfinslightly falcate; apexofpectoral broadly pointed in small specimens, slightly

more

acute in larger individuals; inner corner of pectoral

narrowly rounded;

length of pelvic fin

from

two-thirds to four-fifths length of anal fin; length of pelvic fin base

from

five-ninths to three-fourths length of anal fin base; anterior

margin

of pelvic fin straight or slightly convex;

distal

margin

ofpelvic veryslightly falcate; analfin

from

one-tenth to one-third again as long as pelvicfin; lengthof analfin base one- fourth to four-ninths again as long as pectoral

and

pelvic fin bases

and from

three-fifths again to nearly twice aslong as second dorsal finbase;heightofanalfinone-fifth toone-fourthgreater than height of second dorsal fin; length of caudal fin

from

one-fourth to nearly one-third of total

body

length;

upper margin

of caudal fin evenly convex; terminal partof caudalslightly lessthan one-fourthof total length of fin; lower posterior

margin

of terminal part of caudal fin nearly straight or slightly falcate;

both

terminal

and

lower apices ofcaudal broadly pointed;lower lobe ofcaudal appearingrelatively

narrow and

long, particularly in larger individuals,the distance

from

the angle included

by

the

upper and

lowercaudallobes totipof latter going about

1%

timesin anterior

margin

oflowercaudal lobe;lower caudallobe

about

one-third aslongas

upper

lobe;lower caudal lobe rather erect, sloping posteriorly at

about

a 25 to 30° angle

from

a

HAMMERHEAD SHARKS — ^GILBERT 59